Articulated robots formed by coupling a plurality of arm units are conventionally known. For example, Patent Document 1 discloses an articulated robot including a plurality of arm units. Each of the plurality of arm units is comprised of a circular cylindrical base shaft part having the same diameter as a pedestal, a first arm member coupled to the base shaft part to be rotatable via a ball bearing inside an arm placing groove of D-shape formed in the base shaft part, and a second arm member rotatably coupled to the first arm member. The base shaft part of one of the plurality of arm units is detachably joined to the base shaft part of another arm unit. According to this articulated robot, its effect of being a multi-arm robot including a plurality of arm units in basic, and also becoming a single-arm robot provided with only a single arm unit as needed is stated.